1. Field of the Invention
Methods consistent with the present invention relate to a beacon scheduling method in a network system. More particularly, the present invention relates to a beacon scheduling method of a router to prevent beacon collisions in a network system.
2. Description of the Related Art
In a ZigBee network topology, nodes in a network system are classified to a ZigBee coordinator (ZC), a ZigBee router (ZR), and a ZigBee end device (ZE).
The ZC is on the top of a tree structure and manages the tree. The ZR is below the ZC and responsible to relay a beacon transmitted from the ZC to its child so that the tree structure can be expanded.
The ZE is at the bottom of the network topology. The ZE synchronizes using the beacon transmitted from the ZR and the ZC, and performs communication.
To form such a tree structure, ZRs need to relay beacons received from ZCs to their child. At this time, if the transmission point of the beacons is randomly selected by the ZRs, the beacons are subject to collisions at the child. These beacon collisions block the communications between the nodes.
FIG. 1 illustrates a conventional beacon scheduling method. According to ZigBee NWK v.0.92 (02130r9ZB_NWK_Network-Specification V092), in case that a ZR is connected as a child to a parent which regularly transmits beacons in the tree topology, the ZR schedules its beacons transmission by tracking the beacons of the parent prior to its beacon transmission to its child, and transmitting its beacons by intervals of a beacon Tx offset.
FIGS. 2A and 2B illustrate a problem of the conventional beacon scheduling method.
It is assumed that two children (child 1 and child 2) are connected to the same parent and receive beacons from the parent but do not know each other in their respective regions.
Referring first to FIG. 2A, as the child 1 and the child 2 cannot track beacons of the other, the same beacon Tx offset is used based on the beacons of the parent.
Referring to FIG. 2B, in the hatched area where the coverages of the child 1 and the child 2 overlap, the beacons from the child 1 and the child 2 are collided. As a result, any child within the overlapping region cannot receive the beacons from the child 1 and the child 2.